Background

Head and Neck Squamous Cell Carcinoma (HNSCC) is a malignant tumor that occurs in the oral cavity, pharynx, and larynx, and is a representative cancer that lowers the survival rate of patients. This disease is particularly characterized by a dramatic difference in prognosis depending on whether the patient is positive for Human Papillomavirus (HPV). HPV-positive patients have a good prognosis due to their good response to treatment, but HPV-negative patients have strong resistance to treatment and extremely low survival rates. Previous studies have focused on elucidating the heterogeneity of tumors using genomic analysis or single-cell transcriptomic analysis. However, these analytical methods have limitations in fully showing the spatial information of tissues and cell-to-cell interactions. In particular, there is an urgent need for research to elucidate where cells in a partial Epithelial-to-Mesenchymal Transition (pEMT) state, which is an incomplete transformation of cancer cells from epithelial cells to mesenchymal cells, are located.

Key Findings

To address this, the researchers introduced spatial transcriptomics technology and conducted a detailed analysis of patient tissue samples. As a result, it was revealed that pEMT cancer cells are not randomly distributed within the tumor, but are arranged in two distinct spatial patterns. The first pattern is a localized arrangement of pEMT cells at the edge of the tumor, which is the leading edge of invasion. The cells in this region were closely associated with surrounding fibroblasts, and it was observed that the Transforming Growth Factor-beta (TGF-β) signaling pathway induced this association. The second pattern is an alternative core architecture in which pEMT cells are widely distributed throughout the tumor core. This core pattern was closely associated with macrophages or neutrophils, which induce immune suppression within the tumor. Interestingly, patients with this core pEMT pattern had significantly poorer overall survival compared to patients with the edge pattern. In contrast, in HPV-positive tumors, hypoxia-related signals were activated along with abundant immune cell infiltration, but the distribution of pEMT cells was extremely rare. As a result, it means that the pEMT program in HPV-negative tumors establishes a much more diverse and sophisticated spatial ecosystem.

Significance and Prospects

This study demonstrates that the spatial location within the head and neck cancer tumor is a critical factor in determining the malignant transformation of cancer cells and the immune environment. Beyond the genetic mutations of cancer cells, the spatial arrangement of the microenvironment in which cells reside is directly related to prognosis. In the future, when establishing HNSCC treatment strategies, it is expected that the introduction of the spatial distribution of pEMT cells in tissues into diagnostic guidelines will be actively discussed, beyond simple molecular subtype classification. For example, for patients with a core pEMT pattern, a precision therapy that combines a therapeutic agent targeting immunosuppressive macrophages or a TGF-β inhibitor with an immune checkpoint inhibitor may be an alternative. However, due to the nature of the study that relies on cross-sectional spatial data of patient samples, it was difficult to track the dynamic changes of cells in real time in response to drug administration. Therefore, it is essential to conduct follow-up studies that prospectively validate the validity of this spatial biomarker in a large-scale clinical trial cohort.